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Behaviour of Multilayer Sheet with Technological Imperfection
No full textIn the civil engineering and mechanical engineering are widely used multilayer composite sheets that are designed with symmetrical structure with respect to sheet mid-surface. As a result of technological imperfections and tolerances the actual structure of the sheet is asymmetrical. The reasons of asymmetry may be many the most important are deviation of orientation angle for each layer, deviation of thickness of each layer and deviation of elastic characteristics. Using Monte-Carlo simulation is numerically analyzed the correlation between standard deviation of different technological tolerances and curvature, torsion of the sheet. Two kind of analysis is done- by taking into account geometrical non-linearity and without i
Determination of the Time of Maximum Power Losses by Load Duration Curve
No full textThe utilization time of maximum power losses (UTL) is a parameter used at determination of the active energy losses in power grids, influencing the accuracy of their calculation. This parameter can be estimated by the maximum load time (MLT), since its values can easily be obtained from the readings of widely employed electricity meters. The known methods allow for UTL determination by the total value of MLT, which leads to considerable errors and ambiguous results. The proposed method is based on the load duration curve (LDC) decomposition into two parts: a base and a delta ones. Theoretically, for the base part the UTL can be calculated without errors. The range of errors for the delta part can be considerably narrowed, which will raise the accuracy of the entire LDC calculation. The delta part, according to the method, is reduced to the maximum of 1, which simplifies the UTL calculation. The method is verified on many groups of electricity consumers. The shape of the reduced LDC-delta can be used for identification of the type of electricity consumer
On Calculation of the Time of Maximum Losses by Load Graph
No full textUtilization time of maximum power losses (UTL) has been applied for determination of energy losses in power grids. UTL is a parameter allowing for accurate estimation of energy losses. Using the maximum load time for UTL determination, better results can be achieved by decomposing the load duration graph (LDG) into two parts: the base and the delta ones. Bearing in mind that the latter occupies a smaller area of the entire LDG, the goal is achieved, since the errors can be caused only by the inaccuracy of delta part calculation. Based on this method it is possible to calculate UTL directly from the load graph and to achieve the same accuracy as with the classical method and with the smaller number of load measurements needed. By modifying this method once again, we can estimate UTL from the load graph based on its bearing points which are bending and flex points of the load time curve. The load time graph is decomposed into columns, each of them being contained between two neighboring bearing points. The UTL of each column is calculated to obtain the total UTL, which is the sought for value. The UTL of a column takes into account the minimum load value within the column, the maximum load time and the UTL of its upper part, both of the last quantities depending on the degree of the load curve diversion from a straight line
The Effect of Small Additions of a Liquid-Crystalline Polymer on the Mechanical Properties of Polyethylene
No full textResults of an investigation into the mechanical properties of polyethylene with small, no more than 3 wt.%, additions of a thermotropic liquid-crystalline polymer (LCP) are reported. Experimental data on the influence of LCP additions on the tensile stress–strain diagram, elastic modulus, long-term (up to a 1000-h) creep, and creep recovery after unloading of the specimens are obtained. The elastic properties of the materials are analyzed taking into account the effect of self-reinforcement owing to the formation of extended LCP inclusions. The results obtained are compared with experimental data. Analytical descriptions of the creep and creep recovery of the materials investigated are also presented.
Correlation between the Mechanical Properties and the Amount of Desorpted Water for Composites Based on Recycled Low Density Polyethylene and Linen Yarn Production Waste
No full textThe effect of the amount of sorbed water on the mechanical properties (tensile modulus, tensile strength, unit work of fracture, and characteristic strains) of composites based on a recycled low-density polyethylene, both unmodified and modified with diphenylmethane diisocyanate (DIC), is an a lyzed by statistical methods. The results of tensile tests are found to depend on the amount of sorbed water considerably. The elastic modulus, the unit work of fracture, and the characteristic strains correlate linearly with the amount of water. It is found that the elastic modulus drops after the sorption of water, but then, during the desorption process, it is restored gradually and reaches its initial value after a 30-day drying. This is explained by the plasticizing effect of water on composite materials containing hydrophilic natural fibers. DIC improves the interfacial interaction of the fiber-matrix interface and slows down the desorption of water. The investigations of the main deformational and strength characteristics of the unmodified and modified systems showed that the ad verse effect of water completely disappeared after a 30-day drying. The same conclusion, with a 95% probability, can be drawn from the results of an analysis of variance (ANOVA)
Hugo Gaudig
No full textVācu reformpedagogs Hugo Gaudigs (1860-1923) ietekmējis ne tikai pedagoģijas attīstību Vācijā, bet arī Baltijā. Grāmatā aprakstīti H. Gaudiga kontakti ar Latvijas, Lietuvas un Igaunijas zinātniekiem 20. gs. sākumā. Plašāk aprakstīta H. Gaudiga un viņa līdzstrādnieku viesošanās Latvijā 1922. gada rudenī, kad H. Gaudigs vadīja paraugstundas Rīgas vācu skolās. Grāmatā publicetas H. Gaudiga un viņa kolēģes L. Milleres paraugstundu stenogrammas
Minerālo izejvielu piedevu ietekme uz kordierīta keramikas īpašībām
No full textŠī darba mērķis ir ir izmantot Latvijā pieejamās minerālās izejvielas, lai aizstātu daļu no nepieciešamajām sintētiskajām izejvielām, kas jālieto kordierīta keramikas sintēzei, un izpētītu šo izejvielu ietekmi uz iegūtās keramikas īpašībām
Diarilēteru sintēze c-h aktivācijas ceļā
No full textIegūti jauna tipa platīna kompleksi. Pārbaudīta iegūto kompleksu reaģētspēja reducējošās eliminēšanas
reakcijā
Ar triazoliem konjugētu mono- un oligosaharīdu sintēze
No full textAprakstīta dažādu cukuru-triazolu konjugātu sintēz